Developmental expression of a functional TASK-1 2P domain K+ channel in embryonic chick heart
Background K+ channels are the principal determinants of the resting membrane potential (RMP) in cardiac myocytes and thus, influence the magnitude and time course of the action potential (AP).
Methods: RT-PCR and in situ hybridization are used to study the distribution of TASK-1 and whole-cell patch clamp technique is employed to determine the functional expression of TASK-1 in embryonic chick heart.
Results: Chicken TASK-1 was expressed in the early tubular heart, then substantially decreased in the ventricles by embryonic day 5 (ED5), but remained relatively high in ED5 and ED11 atria. Unlike TASK-1, TASK-3 was uniformly expressed in heart at all developmental stages.
In situ hybridization studies further revealed that TASK-1 was expressed throughout myocardium at Hamilton-Hamburger stages 11 and 18 (S11 &S18) heart. In ED11 heart, TASK-1 expression was more restricted to atria.
Consistent with TASK-1 expression data, patch clamp studies indicated that there was little TASK-1 current, as measured by the difference currents between pH 8.4 and pH 7.4, in ED5 and ED11 ventricular myocytes. However, TASK-1 current was present in the early embryonic heart and ED11 atrial myocytes.
TASK-1 currents were also identified as 3 uM anandamide-sensitive currents. 3 uM anandamide reduced TASK-1 currents by about 58% in ED11 atrial myocytes.
Zn2+ (100 uM) which selectively inhibits TASK-3 channel at this concentration had no effect on TASK currents. In ED11 ventricle where TASK-1 expression was down-regulated, IK1 was about 5 times greater than in ED11 atrial myocytes.
Conclusion: Functional TASK-1 channels are differentially expressed in the developing chick heart and TASK-1 channels contribute to background K+ conductance in the early tubular embryonic heart and in atria.
TASK-1 channels act as a contributor to background K+ current to modulate the cardiac excitability in the embryonic heart that expresses little IK1.
Author: Hengtao ZhangJeremy ParkerNeal ShepherdTony Creazzo
Credits/Source: Journal of Biomedical Science 2009, 16:104
Published on: 2009-11-23
Copyright by the authors listed above - made available via BioMedCentral (Open Access). Please
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